<template>
  <ul class="list" >
    <li
      class="item"
      :key="item"
      :ref="item"
      v-for="item of letters"
      @touchstart="handelTouchStart"
      @touchmove="handelTouchMove"
      @touchend="handelTouchEnd"
      @click="handelLetterClick"
    >{{item}}</li>
  </ul>
</template>

<script>
    export default {
        name: "CityAlphabet",
      props:{
          cities:Object
      },
      data(){
          return {
            touchStatus:false,
            startY:0,
            timer:null
          }
      },
      updated(){
        this.startY = this.$refs["A"][0].offsetTop
      },
      computed:{
          letters(){
            const letters = []
            for (let i in this.cities) {
              letters.push(i)
            }
            return letters
          }
      },
      methods : {
        handelLetterClick (e){
          this.$emit("change",e.target.innerText)
        },
        handelTouchStart(){
            this.touchStatus = true
        },
        handelTouchMove(e){
          if(this.touchStatus){
            if(this.timer){
              clearTimeout(this.timer)
            }
            this.timer=setTimeout(()=>{
              const touchY=e.touches[0].clientY - 79
              const index = Math.floor((touchY - this.startY) / 20)
              if(index >= 0 && index < this.letters.length ){
                this.$emit("change",this.letters[index])
                // console.log(index)
              }
            },16)

          }
        },
        handelTouchEnd(){

        }
      }
    }
</script>

<style lang="stylus" scoped>
  @import "~css/varibles.styl"
  .list
    display :flex
    flex-direction :column
    justify-content :center
    position: absolute;
    top:1.58rem
    right:0
    bottom :0
    width :.4rem
    .item
      line-height :.4rem
      text-align : center
      color:$bgColor
</style>
